A mobile app claiming to be “as effective as the pill” has been reported to Swedish authorities after 37 women claimed to have gotten pregnant while using the app last year.

The Natural Cycles app tracks the changes in a woman’s body temperature over her menstrual cycle to predict days with the lowest risk of pregnancy. It made headlines last year when it became the first certified app of its kind, after being approved as a medical device for contraception by German-based certification body TÜV SÜD.

However, midwives at Stockholm’s Södersjukhuset hospital have reported the app to Sweden’s Medical Products Agency after 37 women using the app got pregnant last year, SVT reports.

The creators of the app have claimed the app is as effective as the contraceptive pill after a study from September in which 22,785 women found the app was 93 percent effective in preventing pregnancies. According to the Mail Online, British users of the app soared to 125,000 last year. The number of Australian users is unknown.

In a statement to SVT, Natural Cycles said: “No contraception is 100 percent and unwanted pregnancies is an unfortunate risk with any contraception.”

“To have 37 unwanted pregnancies out of the 668 mentioned in this study at Södersjukhuset means that 5.5 percent of women who stated they used Natural Cycles also had an unwanted pregnancy.”

“This is in line with what we communicate as the risk of unwanted pregnancy with typical use and which is comparable to other types of contraception.”